refactor generic

[xuhuanzy]

1. std.ConstTpl语义扩展为 TS 的 const, 即在泛型推断中固定所有字面量而不只限于 boolean/string/int
2. 现在泛型推断中字面量会根据上下文自动宽化
3. @type在绑定泛型时会尽量展开为最佳形状

            ---@alias Extract<T, U> T extends U and T or never
            ---@alias KeepA<T> Extract<T, "a">
            ---@alias ForwardConditional<T> KeepA<T>

            ---@generic T
            local function f()
                ---@type ForwardConditional<T>
                local cond -- is `Extract<T,"a">`
            end

[xuhuanzy]

/gemini review

[xuhuanzy]

/gemini review

[xuhuanzy]

/gemini review

[xuhuanzy]

/gemini review